I think the wire crossing at 90 degree is a little too deep. It will however insure that the smallest amount of wires are touching.
Honestly, I had a competition grade audio system. Wires (audio and power) ran down same side of the car, I used 1/0ga to go to 4 batteries in the trunk. Now the signal was sent throught fiber optics so that could not absorb any possible current. In the back I had 6 amps total, and a huge spagetti mess (not a total mess, wires were secured by zip ties and srewed down) of rca's (mostly Y's for the subs) and 8ga wires powering my amps (each sub amp had 2 8ga pos and neg inputs) I had no Engine whine whatsoever.
I would run the cables down differnt sides, once your there, dont have spagetti but dont worry to much about noise from a few wires. You are better off doing it right the first time but I would not get carried away. And yes speaker wires can pic up noise too.
